The invention relates to a feed additive used for weaned piglets. The feed additive used for the weaned piglets comprises the following ingredients in parts by weight: 2-10 parts of sodium butyrate, 5-20 parts of mannan oligosaccharides, 2-10 parts of a bacillus subtilis preparation, and 900-1000 parts of a carrier. Compared with the prior art, the ingredients of the feed additive are cooperated so as to promote growth and development of weaned piglets; and the feed additive has relatively good preventive and therapeutic effects on piglet diarrhea so that the feed additive is capable of replacing antibiotics such as aureomycin and so on so as to reduce usage of the antibiotics; moreover, the feed additive is also capable of improving intestinal probiotic environment of the weaned piglets.The feed additive used for the weaned piglets is free of toxic and side effects, and has good development prospects.